The invention relates to signal-seeking radio receivers and in particular to stepping radio receivers for production of audio signals from radio frequency signals, which receivers are capable of tuning to several separate channels on a plurality of bands. The invention disclosed and claimed herein can be considered to be an improvement on the invention of U.S. Pat. No. 3,665,318 to Hoffman et al. In prior art patents, such as the Hoffman et al patent, band selection was accomplished through the use of a patch panel in which there was one wire associated with each channel. On the end of the wire was a connecting element which fit over pins associated with each band. For each channel there was one pin associated with each band whereby selection could be readily made by placing the wire and connector corresponding to a channel on the pin corresponding to the band desired for that channel. For a two band receiver having only a few channels, this technique functioned without appreciable difficulty. However, when it was desired to have 16 channels and three bands, this technique required 16 wires and connectors at the end thereof together with 48 pins to which the wires could be connected to select bands.
One prior art device of this type substituted for wires and connectors 3 position switches to select the band for each channel. This alternative is disclosed in U.S. Pat. No. 3,824,475 to Peter W. Pflasterer. A device in the television field which selected bands with a 3 position switch is shown in U.S. Pat. No. 3,596,183. Band selection in U.S. Pat. No. 3,873,924 to Fathauer was accomplished by placing the pins associated with a crystal into either one or another crystal pin socket. Here again, while this technique functioned tolerably for two band receivers, difficulty is encountered when it is desired to expand the system to handle three bands.
Another problem encountered in prior art signal-seeking receivers is the tuning of the front end of the receiver. Stepping radio receivers which listen to several separate channels normally require a relatively broad tuned front end in order to accept all of the signals in the band of operation. Difficulty is encountered in designing broad tuned circuits without having adverse effects associated with such designs. To overcome this problem, the certain receivers of the prior art have used variable reactance elements in the tuned circuits in the front end of the receiver. The tuned circuits are then varied to correspond with the desired frequency. In this way a much narrower bandwidth front end circuit can be utilized. However, alignment of the tuning of the front end then becomes a problem and the expense of the additional circuitry adds a substantial cost to the product.
U.S. Pat. No. 3,873,924 to Fathauer discloses a circuit for varying the tuning of the front end of the circuit in response to the local oscillator frequency. U.S. Pat. No. 3,596,183 also shows the use of tuned circuits which are varied in response to a signal corresponding to the oscillator frequency. Neither the use of a broad band front end fixed tuned filter nor a narrow band variable tuned filter has been able to produce a quality receiver at a low cost.